Preheat the Oven: Preheat your oven to 400°F (200°C).
Cook the Beef: In a large skillet, heat olive oil over medium heat. Add the diced onion and carrots, cooking until softened (about 5 minutes). Stir in the minced garlic and ground beef, cooking until the beef is browned. Drain excess fat.
Add Flavor: Stir in the tomato paste, beef broth, Worcestershire sauce, and frozen peas. Season with salt and pepper. Simmer for about 10 minutes until the mixture thickens slightly.
Assemble: Transfer the beef mixture into a baking dish. Spread the mashed potatoes evenly over the top, smoothing out with a spatula.
Bake: Place the dish in the preheated oven and bake for 25-30 minutes, or until the mashed potatoes are golden brown and the filling is bubbling.
Serve: Remove from the oven, let cool for a few minutes, then garnish with fresh parsley if desired. Serve hot.